Colony-stimulating factors (CSFs) are trace glycoproteins found in serum, urine and tissues which are required for the survival, growth and differentiation of hematopoietic progenitor cells in culture. Their physiologic role in hematopoiesis is uncertain, however, and little is known about their structure or mechanism of action. Several human cell lines produce CSFs in culture and the serum-free medium conditioned by these cells provides a convenient starting material for purification. The CSF(s) from a prototype cell line will be purified and characterized. The amino acid sequence of the CSF(s) will be determined and these will be used to generate the sequence of the corresponding mRNA. These studies will provide information about the structure, biosynthesis and secretion of the proteins. Pure CSF will also be used to generate monoclonal antibodies, useful in further purification, immunoassay, and studies of physiology. Finally, the physiology of the pure CSFs will be investigated using hematopoietic colony growth, techniques to determine receptor binding and function, and studies using antibody neutralization. The eventual use of pure CSFs, pure progenitor populations and purified receptors will allow dissection of the role(s) of CSF in the regulation of hematopoiesis.